Spontaneous regression of B220^low cells in the blood of Eμ-myc mice. (A) Blood tumor load was assessed by flow cytometry. Dot plots are representative of blood stained for B220 and IgM expression. Oval gates identify B220^low populations in Eμ-myc mice. (B) Longitudinal analysis of tumor load in peripheral blood of Eμ-myc or WT mice. Each point (·) represents percentage of B220^low cells in the blood of individual Eμ-myc mice. Mice were sacrificed after developing signs of disease. Diamond represents mean tumor load per time point and 95% confidence limit. Mean percentage of B220^low cells in the blood of WT mice is represented by a black line. (C) Number of B220^low cells in the peripheral blood of Eμ-myc or WT mice. Concentration of tumor cell in the blood was calculated by multiplying the number of blood lymphocytes determined by an animal blood counter and percentage of B220^low blood cells assessed by flow cytometry. Data represent mean tumor load per time point and 95% confidence limit. (D) Percentage ± standard deviation (SD) of B220^low cell subtypes in the blood of Eμ-myc mice (n = 10 per time-point) and WT mice (n = 5) at indicated age: IgM⁻ (gray bars), IgM⁺ (white bars). (E) Longitudinal analysis of the B220^low cells in spleen, thymus, bone marrow, and lymph node of Eμ-myc mice. Mean percentage ±SD of IgM⁻B220^low (gray bars) and IgM⁺B220^low (white bars) cells in the indicated organs of Eμ-myc mice (n = 10 per time point) and WT mice (n = 5) before 41 days of age (early), between 41 and 65 days of age (regression), and post–65 days of age (late) is shown. d, day.